Figure 3.

Combined linkage and association mapping identifies ZmTps21 as a candidate β-selinene synthase. A, Major mQTL for β-costic acid production detected on chromosome 9 by CIM using IBM RILs. The inset shows comparative association analysis of the IBM RIL β-costic acid levels using the GLM and 173,984 SNPs. The most statistically significant SNP is located at position 127,854,265 on chromosome 9 (B73 RefGen_v2), with the dashed line denoting the 5% Bonferroni correction. cM, Centimorgan. B, Quantile-quantile plot for the association analysis of β-costic acid levels in the Goodman diversity panel. C, Manhattan plot of the association analysis (MLM) of β-costic acid levels in replicate 1 of the Goodman diversity panel following 3 d of fungal elicitation. The dashed line denotes the 5% Bonferroni-corrected threshold for 246,477 SNP markers, with the most statistically significant SNP located at position 127,858,963 (B73 RefGen_v2) on chromosome 9. D, Location of the candidate gene ZmTps21 on the physical map supported by both linkage analysis and association analysis. E, Fine-mapping with IBM NILs; B73 and Mo17 chromosomal segments are represented by blue and red, respectively. β-Costic acid chemotypes of IBM NILs are indicated as GC/EI-MS traces (m/z = 233). F, Agarose gel PCR-amplified products demonstrate a cDNA length polymorphism between B73 Zmtps21 and Mo17 ZmTps21. G, Diagrammatic structures of B73 Zmtps21 and Mo17 ZmTps21 genes based on sequencing. Exons and introns are denoted as rectangular bars and black lines, respectively. The dashed rectangle indicates the missing B73 genomic DNA and the relative positions of encoded conserved RXR and DDXXD motifs for terpene cyclase activity.